A former San Diego science honors student dressed head-to-foot in body armor and brandishing three weapons opened fire in a packed movie theater in a Denver suburb early Friday, killing 12 people and wounding 58 in one of the worst mass shootings in U.S. history, authorities said.

The suspect, James Eagan Holmes, 24, was detained outside the Aurora theater shortly after the attack. He told police that he had booby-trapped his apartment — about four miles away — with explosives, pitting authorities against a dangerous jigsaw puzzle that had yet to be disarmed late Friday.

No motive for the deadly spree has been pinpointed, leaving people who know the young scholar baffled. His parents and teenage sister, who were awakened with the news at their Rancho Peñasquitos home, asked for privacy during this difficult time. An attorney for the family did not take questions during a Friday evening news conference in front of the two-story house.

Holmes’ mother, a registered nurse, was secluded inside the dwelling Friday with other family members, while his father, a software engineer, flew to Denver.

The FBI said there was no indication of terrorism ties; Holmes is believed to have acted alone. FBI agents in San Diego were assisting with the investigation as needed.

“This is the act, apparently, of a very deranged mind,” said Gov. John Hickenlooper of Colorado.

Holmes, who graduated from Westview High School in Torrey Highlands in 2006, was pursuing a Ph.D. in the neuroscience program at the University of Colorado’s Anschutz Medical Campus in Denver before dropping out last month due to academic reasons, school officials said.

New York City Police Commissioner Raymond Kelly, who was briefed on the investigation, said: “He has his hair painted red. He said he was the Joker, obviously the enemy of Batman.”

‘Reload and shoot’

Police and witnesses described a nightmare that unfolded in Century 16 theater No. 9, where a sold-out crowd had gathered for a midnight showing of the new Batman movie, “The Dark Knight Rises.”

A federal law enforcement official, speaking on condition of anonymity, said Holmes bought a ticket to the show, went into the theater as part of the crowd, pretended to take a phone call and propped open a side exit door. He then allegedly donned body armor and a gas mask before returning to the theater for his attack.

At first he was just a silhouette, taken by some in the audience for a stunt as part of one of the summer’s most highly anticipated films.

But then, authorities said, he threw gas canisters that filled the theater with smoke and, in the confusing haze between Hollywood fantasy and terrifying reality, opened fire as people screamed and dove for cover.

Holmes allegedly used an AR-15 assault rifle, a Remington 12-gauge shotgun and a .40-caliber Glock handgun. He marched up the aisle in the stadium-style theater and picked off those who tried to flee, witnesses said.

“He would reload and shoot, and anyone who would try to leave would just get killed,” said Jennifer Seeger, 25, adding that bullet casings landed on her head and burned her forehead.